Answer to Question #142645 in General Chemistry for Sohum patel

Question

If your melting point was 158 oC in the experiment what compound caused this melting point
and why do you think you did not produce acetylsalicylic acid? Research your result.

Answer 1

Aspirin is the common name for the compound acetylsalicylic acid. Preparation of the acid involves reaction of salicylic acid$(C_7H_6O_3)$ with excess acetic anhydride$(C_4H_6O_3)$ . Phosphoric acid $(H_3PO_4)$ , a strong acid, in most instances is used a a catalyst,which speeds up the reaction. The excess acetic acid will be quenched with 

the addition of water. The aspirin product is not very soluble in water hence  precipitates with the addition of water.

The equation for the reaction is;

$C_7H_6O_3+C_4H_6O_3\underrightarrow{H_3PO_4}C_9H_8O_4+C_2H_4O_2$

The melting point range of pure aspirin is $138-140°C$ and the melting point range of the salicylic acid 

starting material is $158-161°C$ .

Addition of impurities lowers the melting point of the aspirin produced.

In this case, phosphoric acid, a catalyst speeds up the rate of the reaction hence attaining the required melting point.